Method of operating a photometric analysis apparatus

ABSTRACT

The present invention relates to the field of photometric analysis, particularly to photometric analysis apparatuses which use disk-shaped rotors, in which the rotors are loaded automatically.

[0001] The present invention relates to photometric analysis apparatusof the type which uses disk-shaped rotors, in which the rotors areloaded automatically.

[0002] Photometric analysis apparatus using disk-shaped rotors is widelyknown. The disk-shaped rotors, which are generally made of plasticsmaterial, comprise a plurality of cuvettes arranged radially around acentral hole. The cuvettes provide a plurality of communicating chambersseparated by partitions. The rotor is connected to a hub connected to amotor which imparts rotary motion to the rotor. A sample to be analyzedand the appropriate reagents are introduced into each cuvette. Thereagents are mixed by centrifugal effect when the rotor reaches apredetermined speed of rotation. In the next step, the individualcuvettes are brought sequentially into alignment with optical analysismeans by programmed rotation of the rotor.

[0003] The general structure of the rotors and of the photometricanalysis apparatus is known per se and will therefore not be describedin greater detail herein. The function of the rotors and the way inwhich they interact with the sensors for analyzing the samples aredescribed, for example, in the Applicant's Italian patent applicationNo. 20560A/83.

[0004] This photometric analysis apparatus is arranged to perform alarge number of analyses in sequence. Clearly therefore, an essentialcharacteristic of these machines is speed of operation. However, speedof operation must be combined with considerable precision in theexecution of all of the steps of the analysis process from the loadingof the rotors to their positioning on the hub, and to the perfectalignment of the cuvettes with the optical analysis means. A perfect andrepeatable relationship between the positions of the cuvette and of thephotoanalysis means is in fact essential for the reliability of themeasurement.

[0005] The problem upon which the present invention is based is that ofproviding analysis apparatus having an automatic rotor-loading systemwhich permits fast and accurate operation.

[0006] This problem is solved by photometric analysis apparatus and by arotor as claimed in the appended claims.

[0007] Further characteristics and advantages of the photometricanalysis apparatus of the present invention will become clearer from thedescription of an embodiment thereof given by way of non-limitingexample below with reference to the following drawings:

[0008]FIG. 1 is a partially-sectioned, perspective view of thephotometric analysis apparatus of the present invention;

[0009]FIG. 2 is a perspective view of a pincer for loading the rotorsaccording to the present invention;

[0010]FIG. 3 is a partially-sectioned plan view of the pincer of FIG. 2;

[0011]FIG. 4 is a plan view of the rotor of the present invention;

[0012]FIGS. 5a-5 d show the sequence of steps for loading the rotors onthe analysis means, showing the apparatus of FIG. 1 in section;

[0013]FIG. 6 is a side view showing, in section, the hub on which therotor is fixed in the analysis apparatus.

[0014] With reference to the above-mentioned drawings, the photometricanalysis apparatus of the present invention is generally indicated 1.The apparatus comprises a hopper 2 for the loading of the rotors 3, anda pincer 4 for automatically transferring the rotors from a pick-upposition beside the hopper 2 to the analysis unit 5, in the region ofthe optical analysis means (not shown in the drawings). The analysisunit 5 comprises means for imparting rotary motion to the rotor 3, andoptical analysis means. The means for rotating the rotor comprise anelectric motor connected to a transmission shaft 5 a, to the upper endof which a hub 5 b is fixed. The rotor 3 is positioned on the hub. It isextremely important to ensure the correct angular positioning of therotor 3 on the hub so as to achieve perfect alignment of the cuvetteswith the optical analysis means. The analysis unit 5, however, is of atype the general structure of which is widely known.

[0015] The apparatus 1 also comprises a plate 6 supported for sliding onthe apparatus beneath the hopper 2. The plate 6 is moved by an electricactuator and can adopt a first position beneath the hopper 2 and inalignment with the longitudinal axis thereof, and a second positionbeneath the pick-up position of the pincer 4.

[0016] The plate 6 is circular and has dimensions substantiallycorresponding to those of the rotor 3. The plate 6 also has raised edgesand, centrally, a pin 6′ to be housed in the central hole of the rotor3. Triangular raised portions formed on the surface of the plate 6 arearranged radially around the pin 6′. These triangular raised portionsare intended to engage in the angular spaces formed between one cuvetteand another on the lower surface of the rotor 3 (see FIG. 4).

[0017] With reference to FIGS. 2 and 3, the pincer 4 comprises an arm 7and two semicircular and symmetrical claws 7′, 7″. The claws 7′, 7″ aresupported movably and jointly on the arm 7 by means of a hinge 7 a.

[0018] The arm 7 comprises a tongue 8 which projects towards the centreof symmetry of the claws 7′, 7″. At this centre of symmetry, the tongue8 has a downwardly-projecting finger 9 the function of which will becomeclear from the following description.

[0019] The end of the arm 7 remote from the tongue 8 comprises means 10for engagement on an actuator (not shown in the drawing) which providesfor the movement of the pincer 4 from the region in which the rotors arepicked up to the analysis region, as well as for a vertical movementthereof to enable the rotor to be engaged and released.

[0020] Each claw 7′, 7″ comprises a groove 11 for engaging the edges ofthe rotor 3. On each claw 7′, 7″, there is a tooth 11 a, the teeth 11 apreferably being in symmetrical positions within the grooves 11. Theteeth 11 a are preferably substantially wedge-shaped.

[0021] In the vicinity of their articulation point, the claws 7′, 7″have hooks 12, 12′ which extend towards the centre of symmetry of theclaws, parallel to the tongue 8. The hooks 12, 12′ hold resilientjoining means 13 such as, for example, a rubber band.

[0022] The claws 7′, 7″ further comprise elements 14, 14′ alsoprojecting in the vicinity of the articulation point but in the oppositedirection to the hooks 12, 12′. These projecting elements are arrangedin a manner such as to be crossed, so that the element 14 projectingfrom the left-hand claw 7′ is disposed on the right-hand side of theelement 14′ projecting from the right-hand claw 7″. The projectingelements 14, 14′ also have bulbous ends 15, 15′.

[0023] In the vicinity of the engagement means 10 but on the oppositeside thereto, the arm 7 supports an electromagnet 16 connected to acurrent generator (not shown in the drawing). An actuator element 17terminating in a drop-shaped end 18 is connected to the electromagnet16. In the rest condition, the drop-shaped end 18 is disposed in thespace between the projecting elements 14, 14′, as shown in FIG. 3.

[0024] With reference to FIG. 4, the rotor 3 is disk-shaped and isgenerally made of plastics material. Cuvettes 19 for holding the samplesto be analyzed and the reagents are supported radially on its lowersurface.

[0025] The rotor 3 comprises a central hole 20 for engaging the hub ofthe analysis apparatus. The central hole 20 may have various shapes. Itis preferably polygonal, as shown in the drawing, to ensure the correctangular positioning of the rotor on the hub.

[0026] A first notch 21 and a second notch 21′ are formed on theperipheral edge of the rotor 3, and are generally (but not necessarily)disposed at the ends of a diameter of the rotor 3. These notches areintended to be engaged by the teeth 11 a of the pincer 4 to ensure thecorrect angular positioning of the rotor on the pincer and consequentlyin the analysis unit. The shape of these notches substantiallycorresponds to that of the teeth 11 a and is thus preferably V-shaped.The V-shaped notches 21, 21′ also advantageously have one side which ismore inclined than the other to the bisector of the angle formed therebyso as to constitute a type of lead-in for the teeth 11 a during thepicking-up of the rotor by the pincer 4.

[0027] A third notch 22 which may be of various shapes, for example,trapezoidal as in FIG. 4, is also formed on the peripheral edge of therotor 3. It is essential for this notch 22 to be in an asymmetricposition relative to the first two notches 21, 21′, that is, for thecircle arc included between the first notch 21 and the third notch 22 tohave a different length, for example, a shorter length than the circlearc included between the third notch 22 and the second notch 21′.

[0028] The hopper 2 is substantially cylindrical and is open at its twoends. The inside diameter of the hopper 2 substantially corresponds toor is slightly greater than that of the rotors 3. The hopper 2 comprisesasymmetric means for locating the rotors 3 positively in the hopper. Inpractice, the inner surface of the hopper 2 has vertical ribs 23, 23′and 24 corresponding in shape, size and position to the notches 21, 21′and 22 formed on the edge of the rotor 3, respectively.

[0029] In the lower portion of the hopper there is a device 25 forseparating the rotors. This device comprises two pairs of pincers 26,26′ and 27, 27′ disposed one above another on the walls of the hopper.These pincers, which are shaped like arcs of a circle, extend throughthe walls of the hopper 2 so that, in the closed position, they projecttowards the interior of the hopper. When the pincers are in the openposition, on the other hand, they are retracted inside the walls of thehopper. These pincers are operated by means of an electromagnet deviceexactly the same as that described above for the pincer 4 (theelectromagnet 26 a which operates the pincers 26, 26′ is shown in brokenoutline in FIG. 1).

[0030] It should be noted that both the hopper 2 and the plate 6comprise internal electrical resistors (not shown in the drawing) whichhave the function of thermal conditioning of the rotors at thetemperature at which the analysis is performed in the analysis unit 5.This temperature is generally about 37° C. The triangular projectionspresent on the plate 6 also have the purpose of increasing the area ofcontact between the heated plate and the rotor, improving heat-exchangeefficiency.

[0031] Moreover, inside the hopper 2 in the region of the two pairs ofpincers 26, 26′ and 27, 27′, there are optical sensors which can detectthe presence of a rotor at the level both of the lower pair of pincers27, 27′ and of the upper pair of pincers 26, 26′. This information isthen indicated in an appropriate manner, for example, on a controlconsole, to permit human intervention if the hopper is empty or in theevent of a malfunction.

[0032] With reference to FIG. 6, the hub 5 b comprises a hollow body 28(for fixing to the shaft 5 a), the upper portion 28′ of which has across-section of a shape and size substantially corresponding to thoseof the central hole 20 in the rotor 3. At the point at which the hollowbody 28 is joined to its upper portion 28′, there is a projectingannular wall 34 constituting a support point for the rotor 3.

[0033] Substantially triangular clips 29, 29′ project sideways from theupper portion 28′. These clips are articulated, possibly resiliently, onrespective pins 30, 30′ so as to be pivotable about the axes extendingthrough these pins. A push-button 31 arranged concentrically inside thehollow body 28 bears on a spring 32. The push-button 31 projects fromthe top of the upper portion 28′ of the hollow body 28. The cylindricalsurface of the push-button 31 has recesses 33, 33′ in which the innerends of the clips 29, 29′ engage. Clearly, if the push-button 31 ispressed, it will push the inner ends of the clips 29, 29′ downwardscausing the clips to pivot about the respective pins 30, 30′. Theprojecting ends of the clips 29, 29′ are thus retracted into the upperportion 28′ of the hollow body 28. If the push button 31 is released, itwill return to its original position under the effect of the spring 32;the clips 29, 29′ will thus be returned to the starting condition in thesame manner.

[0034] The operation of the rotor-loading device of the presentinvention will now be described, again with reference to the drawings,particularly FIGS. 5a-5 d.

[0035] First of all, the rotors 3 are inserted in the hopper 2 bycausing the notches 21, 21′ 22 to coincide with the respective ribs 23,23′, 24 of the hopper. The separating device 25 will have both pairs ofpincers 26, 26′ and 27, 27′ in the closed position. The stack of rotors3 thus bears on the upper pair of pincers 26, 26′. At this point, theplate 6 is aligned underneath the hopper 2, and the pincer 4 is arrangedin the position for picking up a rotor.

[0036] A first and essential advantage of the apparatus of the presentinvention should be noted. As stated above, the rotor 3 is loaded bycausing the notches 21, 21′ and the third notch 22 which is disposed inan asymmetric position relative to the other two, to coincide with theribs 23, 23′ 24 of the hopper, respectively. The presence of anasymmetric notch-rib coupling thus clearly excludes the possibility ofthe rotors being loaded upside down, which would not only invalidate thesubsequent analysis but would also cause malfunctioning of the loadingdevice.

[0037] Moreover, the correct angular positioning of the ribs 23, 23′, 24determines the final orientation of the rotors 3 on the analysis unit 5(the alignment of the cuvettes 19 with the optical analysis means).

[0038] To return to the description of the operation of the apparatus 1,at this point, the upper pair of pincers 26, 26′ of the separatingdevice 25 opens, allowing the stack of rotors to fall onto the lowerpair of pincers 27, 27′ as shown in FIG. 5a.

[0039] The next step provides for the re-closure of the upper pair ofpincers 26, 26′ which are interposed between the lowermost rotor 3 andthe overlying stack of rotors, separating the lower rotor. As a resultof the opening of the lower pair of pincers 27, 27′, the lower rotorfalls onto the plate 6 (see FIG. 5b). As stated above, the lower surfaceof the rotor 3, on which the cuvettes 19 are disposed, engages thetriangular raised portions projecting from the plate 6, which arearranged in the triangular spaces between one cuvette and another. Thecorrect angular orientation of the rotors is thus maintained.

[0040] At this point, the plate 6 is translated by the actuator (notshown in the drawings) to the pick-up position of the pincer 4 (see FIG.5c). At the same time, the lower pair of pincers 27, 27′ of the hopper 2is closed, re-establishing the starting condition.

[0041] The pincer 4, the claws 7′, 7″ of which are open at this point,is moved vertically downwards by the respective actuator so as to placethe grooves 11 in a position coplanar with the rotor 3. The claws 7′, 7″then close, engaging the outer edge of the rotor. In particular, theteeth 11 a engage the notches 21 and 21′ of the rotor; the correctangular orientation of the rotor 3 is thus also maintained during itstransportation onto the hub 5 b of the analysis unit 5.

[0042] The pincer 4 is then moved vertically upwards, disengaging therotor from the plate 6, and is then rotated to the region of theanalysis unit 5. At this point, the pincer 4 performs a verticaldownward movement. The central hole 20 of the rotor 3 starts to engagethe hub 5 b. At the same time, the finger 9 disposed on the tongue 8 ofthe pincer 4 presses the push-button 31 of the hub 5 b, causing theclips 29, 29′ to be retracted into the upper portion 28′ of the hollowbody 28. The vertical movement of the pincer 4 is then completed untilthe lower surface of the rotor 3 engages the projecting wall 34 of thehub 5 b. The claws 7′, 7″ of the pincer 4 open, releasing the rotor 3and the pincer is then returned to the rotor pick-up position. At themoment when the pincer 4 is raised, the finger 9 stops exerting itspressure on the push-button 31 and the clips 29, 29′ consequently returnto the starting position, pressing against the edges of the central hole20 of the rotor 3. This ensures that the angular orientation of therotor is also constantly correct during the analysis process, duringwhich the rotor is rotated at high speed.

[0043] At the moment when the pincer 4 has reached the rotor pick-upposition again, the rotor-loading cycle can recommence.

[0044] The mechanism for opening and closing the claws of the pincer 4is as follows. The actuator element 17 is retracted in the direction ofthe arrow of FIG. 3 by the effect of the electromagnet 16. Thedrop-shaped end 18 of this actuator element 17 thus acts on the bulbousends 15, 15′ of the projecting elements 14, 14′, causing them to moveapart. The claws 7′, 7″ thus open. When the electromagnet 16 returns theactuator element 17 to its initial position, the resilient joining means13 of the hooks 12, 12′ return the claws 7′, 7″ to the closed position.

[0045] The rotor-loading cycle described above, as well as thesubsequent analytical process, are generally performed by an operatingand control unit (not shown in the drawings) of known type.

[0046] The photometric analysis apparatus of the present invention thushas the advantage of enabling the process to be performed automatically,maximizing the productivity of the apparatus. At the same time, theparticular characteristic of the provision of at least three notchesarranged asymmetrically on the edge of the rotor and complementary tothe ribs of the hopper 2, as well as the presence of the triangularraised portions projecting from the plate 6 and of the teeth 11 a on thepincer 4, ensure considerable precision in the positioning of the rotorrelative to the optical analysis means, which is essential in achievingcorrect analysis.

[0047] Clearly, the embodiment described is only one particularembodiment of the photometric analysis apparatus of the presentinvention to which an expert in the art may apply any modificationsnecessary to adapt it to particular applications without, however,departing from the scope of protection of the present invention.

[0048] In particular, the notches 21, 21′ formed in the edge of therotor may have shapes other than the substantially triangular shapeshown in the drawings. For example, they could be half-moon-shaped ortrapezoidal. Naturally, the respective ribs 23, 23′ of the hopper 2 andthe teeth 11 a of the pincer 4 would also have to be modifiedcorrespondingly.

[0049] The third notch 22 of the rotor may also have a shape other thanthat shown in the drawing. For example, it could have the same shape asthe other two notches 21, 21′.

[0050] In this case, the rib 24 of the hopper would have to be modifiedcorrespondingly.

[0051] The number of notches 21, 21′ (and correspondingly of teeth 11 a)is not necessarily limited to two and it is also possible to have morethan one notch 22. It is, however, essential that the distribution ofthe notches on the peripheral edge of the rotor should give rise to anasymmetric configuration, as explained above.

[0052] In a further embodiment of the present invention, only twonotches (to which only two complementary ribs in the hopper 2correspond) are provided on the edge of the rotor 3. These notches mustnecessarily have different shapes and the circle arc included betweenthem must extend through an angle of less than 180°, so that it is notpossible to identify a plane of symmetry perpendicular to the plane ofthe rotor and extending through its centre. For example, it is possibleto form on the rotor 3 only one of the two V-shaped notches 21, 21′ andthe trapezoidal notch 22. It will thus still be possible to position therotors correctly inside the hopper 2. In this embodiment of the presentinvention, the pincer 4 will also have to be modified by the eliminationof one of the two teeth 11 a and possibly by the provision of a toothcomplementary to the notch 22 of the rotor, on one of the two claws.

[0053] For the purposes of the present invention, it is thus essentialfor the rotor to have at least two asymmetric locating notches havingshapes and positions such that it is not possible to identify a plane ofsymmetry which is perpendicular to the plane in which the rotor lies andwhich extends through the centre thereof. The same number ofcomplementary ribs disposed inside the hopper 2 will correspond to thesenotches.

[0054] According to further variants of the present invention, thecentral hole 20 of the rotor may have shapes other than the polygonalshape shown in the drawing. For example, it may have a D-shaped profileor any other profile in which at least one side is straight. In thiscase, the upper portion 28′ of the hub must also be shaped in acorresponding manner.

[0055] The rotor 3 described above can also clearly be used on any knownphotometric analysis apparatus since the notches formed on its edge donot interfere in any way with the performance of the analysis onconventional analysis apparatus.

[0056] Moreover, the rotor 3 described and claimed can advantageouslyalso be used on manually-loaded analysis apparatus in which a containeris generally provided for the thermal conditioning of the rotors, therotors being taken from the container manually in order for the analysisto be performed. In this case, the thermal conditioning container willhave to be modified suitably by the formation therein of a seat forhousing the rotors, in which at least two ribs of different shapes, forexample, one of the ribs 23, 23′ and the rib 24 will be reproduced. Therotor 3 in turn will have at least two notches, for example, one of thetwo notches 21, 21′ and the notch 22. As explained above, if the rotorhas only two notches, they should be of different shapes and should notlie at the ends of a diameter of the rotor. The advantage of thisembodiment is that the rotors are positioned correctly in the thermalconditioning container. When the operator picks them up in order toplace them on the analysis unit, he will therefore find them alreadycorrectly oriented. The possibility of loading errors is thuseliminated.

1. Photometric analysis apparatus of the type which uses disk-shapedrotors, characterized in that it has a device for loading the rotors (3)on to an analysis unit (5) automatically, the device comprising a hopper(2) for supplying the rotors, the hopper (2) comprising asymmetric meansfor locating the rotors (3) positively in the hopper.
 2. Apparatusaccording to claim 1, in which the asymmetric means for locating therotors positively comprise at least three ribs (23, 23′, 24) arrangedlongitudinally on the inner wall of the hopper (2), the ribscorresponding, respectively, to at least one first notch, one secondnotch and one third notch (21, 21′, 22) formed in the outer edges of therotors (3), the at least three ribs (23, 23′, 24) being arrangedasymmetrically, that is, the circle arc included between a first rib(23) and a second rib (24) having a length different from that of thecircle arc included between the second rib (24) and a third rib (23′).3. Apparatus according to claim 2, in which the at least three ribs (23,23′, 24) have shapes and sizes substantially corresponding,respectively, to the at least one first, one second and one third notch(21, 21′, 22) of the rotor (30).
 4. Apparatus according to any one ofclaims 1 to 3, in which the analysis unit (5) comprises a hub (5 b) forthe rotor (3), clips (29, 29′) projecting laterally from the hub, and apush-button (31) which bears on a spring (32) acting on the clips (29,29′) so that, if the push-button (31) is pressed, it causes the clips(29, 29′) to be retracted into the hub (5 b) whereas, when thepush-button (31) is released, the clips (29, 29′) project laterallyagain.
 5. Apparatus according to any one of claims 1 to 4, comprising apincer (4) for transferring the rotor (3), the pincer being movablebetween a rotor pick-up position and the analysis unit (5), in which thepincer (4) comprises two claws (7′ 7″) articulated movably and jointlyon an arm (7), each claw (7′,7″) having a groove (11) for engaging theedges of the rotor (3), and teeth (11 a) of a shape and sizesubstantially corresponding to those of the at least one first and onesecond notch (21, 21′) of the rotor (3) being disposed in the grooves(11).
 6. Apparatus according to claim 5, in which the arm (7) comprisesa tongue (8) which projects towards the centre of symmetry of the claws(7′, 7″), a downwardly-facing finger (9) being disposed on the tongue(8) at the centre of symmetry, the finger (9) being intended to pressthe push-button (31) of the hub (5 b).
 7. Apparatus according to claim1, in which the asymmetric means for locating rotors positively comprisetwo ribs (23, 24) arranged longitudinally on the inner wall of thehopper (2) and corresponding, respectively, to two notches (21, 22)formed on the outer edges of the rotors (3), in which the ribs (23, 24)have different shapes, and in which the circle arc included between theribs extends through an angle of less than 180°.
 8. Apparatus accordingto any one of claims 1 to 7, in which the hopper (2) has a device (25)for separating the rotors (3), the device comprising two pairs ofpincers (26, 26′, 27, 27′) disposed one above the other on the walls ofthe hopper, the pincers being arranged in a manner such that, in theclosed position, they project towards the interior of the hopper (2)whereas, in the open position, they are retracted into the walls of thehopper (2).
 9. Apparatus according to any one of claims 1 to 8,comprising a plate (6) movable between a position aligned with thelongitudinal axis of the hopper (2) and the position for picking Up therotor (3), in which the plate (6) has, on its upper surface, a pluralityof triangular raised portions arranged radially around a pin (6′). 10.Apparatus according to any one of claims 1 to 9, in which electricalresistors for thermally conditioning the rotors are disposed inside thehopper (2) and the plate (6).
 11. A disk-shaped rotor (3) forphotometric analysis apparatus having a plurality of cuvettes (19)arranged radially on its lower surface and a central hole (20) forengaging the hub (5 b) of the analysis unit (5), characterized in thatat least two asymmetric locating notches are formed on the peripheraledge of the rotor (3) and have shapes and positions such that it is notpossible to identify a plane of symmetry which is perpendicular to theplane in which the rotor lies and which extends through the centrethereof.
 12. A rotor according to claim 11, on the edge of which a firstnotch, a second notch, and a third notch (21, 21′, 22) are formed, thethird notch (22) being arranged in an asymmetric position relative tothe first and second notches (21, 21′) so that the circle arc includedbetween the first notch (21) and the third notch (22) has a lengthdifferent from that of the circle arc included between the third notch(22) and the second notch (21′).
 13. A rotor according to claim 11, onthe edge of which two notches (21, 22) are formed, the notches being ofdifferent shapes and the circle arc included between the two notches(21, 22) extending through an angle of less than 180°.
 14. A rotoraccording to claim 12, in which the first and second notches (21, 21′)are disposed at the ends of a diameter of the rotor (3).
 15. A rotoraccording to claim 12 or claim 14, in which the at least one first notchand the at least one second notch (21, 21′) are V-shaped.
 16. A rotoraccording to claim 15, in which the V-shaped notches (21, 21′) have oneside having a greater inclination than the other to the bisector of theangle formed thereby so as to constitute a type of lead-in for the teeth(11 a) during the picking-up of the rotor by the pincer (4).
 17. A rotoraccording to claim 16, in which the at least one third notch (22) issubstantially trapezoidal.
 18. A rotor according to any one of claims 11to 17, in which the central hole (20) has at least one straight side.19. A rotor according to claim 18, in which the central hole (20) ispolygonal.